1. Field of the Invention
The present invention relates to a supervisory control system, and more particularly, to such a system which utilizes microprocessors for remotely monitoring and controlling at least one operational device, such as a valve, pump, or the like.
2. Setting of the Invention
A long progression of automation efforts have been underway in the pipeline industry and in the petroleum industry as a whole to improve operational efficiency and reduce costs. The net result of this is that large quantities of oil or other valuable fluids are unaccounted for or are not accurately measured due to the inaccurateness of measuring devices or the lack of centralized control. To increase efficiencies, various improvements have been made in pipeline equipment and measurement techniques, such as improved turbine meters, prover loops, LACT units, tank gauging devices, and sensing devices which detect differences in gases and fluids that are passed through a pipeline. All of these devices have improved accuracies and reliabilities; however, there is still a problem in developing a centralized supervisory control system which can be installed in remote locations and used with these improved devices to achieve improved pipeline operations.
A centralized supervisory control system can provide the ability to perform many different command functions, report on the status of various devices, read out analog values or levels and accumulator values, and report certain logging information, etc. Most pipelines currently utilize hardwired sequence controllers, wherein all the commands needed in the operation of a facility, such as a pump station, are cooperative and interlocked together to provide the proper starting and shutdown control necessary for safe and proper operation of the facility. Operational device status, pressures, temperatures, meter readings, and other pertinent information are brought to control panels within the hardwired sequence controller and are displayed and recorded as necessary for the local operation of the facility. If a supervisory control system is to be added to such a sequence controller, then additional control relays, status pick up points, and analog and accumulator outputs need to be provided for interconnection to the supervisory control system. This conversion from local control to a centralized or remote control requires costly rewiring. Further, to change the mode of operation in a control system is sometimes a harder task to perform than it would be if an entirely new system was being installed. For example, newer supervisory control systems usually use low-voltage DC, while older controllers use high-voltage AC. Further, in many cases, there are no provisions for or ability to read vital data needed for the operation of the supervisory control system.
As an example, an operator can read a series of temperatures and pressures and tell if an operational device is running in normally acceptable ranges. It is another matter entirely to have the temperatures and pressures read and sent automatically out to a local display unit on a sequence control panel, and it is even more difficult to gather and format that data for transmittal to a remote location for use by a supervisory control system. This problem, plus the need for new and better control equipment, is the reason why field and equipment costs can account for 50% or more of the cost of a modernization program to install a supervisory control system on a typical pipeline facility.
Supervisory control systems which use new microprocessor technology to aid in pipeline control, but which suffer with the drawbacks of older systems are described in "New Developments in the Electronic Instrumentation and Control of Gas Pipelines" by Dr. John Kendall and published in Energy Processing/Canada January/February 1983; and "Microprocessor Controls Remote Pipeline Sites" by Ernest E. Godsey and published in The Oil and Gas Journal--Jan. 31, 1977.
Another new supervisory control system is called an AMOCAMS 300 or 600 series system which has been produced by Amoco Pipeline Company and is utilized as a hardwired supervisory control system. The AMOCAMS system has been a very successful control system, but is primarily developed for one installation operability and does not have the expandability and flexibility of operation as is sometimes needed. There is a need for a supervisory control system which can be used with or in replacement of the large number of older systems, be they hardwired masters, remote terminal units (RTU's), and new generation equipment. Further, there is a need for a system based upon a microprocessor which is cooperable and comparable with previously existing systems and whose function is to provide enhanced service or the same service as is being performed by the older units.
In designing supervisory control systems, certain design problems are encountered relating to field installations and environments, such as lightning, extreme temperature variations, inexperienced maintenance personnel, the large number of installations, lack of operating power systems, and lack of suitable communication links.
It has been found that lightning damage is the largest single cause of failure of electronic equipment used in field installations as part of a supervisory control system. The factors that contribute to lightning damage include the use of tall antennas, overhead power lines, underground production equipment, underground conduit cables, as well as underground electrical equipment. Usually, upon installation efforts are made to ensure that all electronic devices interconnected to electronic equipment in a physical way are at the same "ground" potential. If extreme care is not taken at the time of installation, then no matter how well a design has been conceived and no matter how well the unit has been tested, the equipment will not be adequately protected from lightning damage.
Another problem encountered is the extreme temperature variations found in field locations, such as temperature variances from -30.degree. F. up to 130.degree. F. If an electronic device, such as a microprocessor, is packaged in an enclosed housing, the temperature inside the housing due to heat buildup from outside sources can become excessive, and if the internal heat generated by the electronic equipment is added then the combined heat buildup can become intolerable causing premature failure of the electronic device. Also, previous experience has taught that continuous fluctuations in temperature causes undesirable stress in the electrical components, solder joints, and PCB connections.
Another problem encountered is that microprocessors are relatively recent inventions and require highly skilled technicians to troubleshoot. Not only must the technician who maintains the microcomputer be highly skilled, but he also must have the proper test equipment for use in remote field locations. Such technicians are often not available to service remotely located field installations, so unskilled people must be relied upon, and such test equipment is delicate and expensive.
Another problem encountered is that the overall number of electronic components has to be carefully considered in the design of a microprocessor-based supervisory control system. "Off the shelf" control systems are usually compromises in flexibility and expandability, and one must be able to accept the design parameters which are to be implemented due to the aforementioned problems inherent in a typical field installation. Such problems can include mounting the off-the-shelf microprocessor package in an above ground metal enclosure and interconnecting it to outputs of control devices, input/output ports, and various end devices such as pressure, differential pressure, and temperature transducers, as well as turbine meters and control valves. All such connections are different and pose unique problems, which usually cannot be met by an "off the shelf" control system.
Another problem encountered is that power networks are not available in remote locations and if they are available, such as in a production field, are usually, at best, undesirable power source for a supervisory control system. Thus, it is preferable to isolate electronic packages from this power network if at all possible.
Further, another problem encountered is that certain remote terminal units (RTU), used as controllers, communicate with a remotely located host computer that controls the entire system and is located from a few feet to many miles away. There are problems in obtaining "right-of-way" for laying interconnecting cables between the remote installations and the host computer. Further, in a production field, there are also problems of numerous cable cuttings due to normal production field activity. If radio communications are utilized, usually, there is a large power demand which, again, can become dependent upon an unpredictable power network.
There is a need for a supervisory control system which can be easily expanded or added to an existing supervisory control system and which has lightning protection, temperature protection, ease of maintenance, expandability, and flexibility in design, can be isolated from a power network, and can utilize reliable communication links over remote distances.
One supervisory control system which has been developed to control a fluid storage facility and includes microprocessors and devices to protect from power surges is disclosed in Moncrief, Jr. et al U.S. Pat. No. 4,387,434. While the control system of Moncrief is an advancement over prior systems, Moncrief does not disclose or suggest a supervisory control system for use in many different applications and which can communicate to a remote location via a radio communications link, utilizing a power source other than the field power supply, and has a complete separation of the remote located devices from the controller to protect from power surges and transients. The system of Moncrief attempts to address the problem associated with power surges but does not suggest or disclose ways to overcome the other above listed problems associated with field installations of supervisory control systems.